The CTC is defined as a tumor cell that circulates through a human peripheral blood flow, and is tumor cell that infiltrates into a blood vessel from a primary cell or a metastatic tumor. If the CTC can be trapped in the same state as that in a blood flow, early detection of cancer or early development of effective medicine can be expected. However, the number of CTCs as small as one per 108 to 109 blood cells included in blood of a metastatic cancer patient, and thus it is difficult to trap only the CTC except for blood cells.
In consideration of the difficulty, a method of separating a blood cell and a cancer cell by utilizing a difference in size between the blood cell and the cancer cell has been examined (for example, refer to Patent Literature 1). In this method, a metal filter is used, and thus a variation in hole size is small. Accordingly, separation of the cancer cell with high separation accuracy and concentration thereof have been expected (for example, refer to Patent Literature 2).
The metal filter disclosed in Patent Literature 2 has a rectangular hole shape, and is typically formed by electro-deposition, electro-casting, or plating using a resist. In a case of manufacturing the metal filter by this method, a plurality of resist islands for formation of a through-hole of the filter are arranged on a substrate to be close to each other on a substrate in the middle of a manufacturing process. Here, when a rinsing liquid flows through a narrow space between resists, a problem such as collapse of a resist pattern formed in an island shape and peeling-off of the resist pattern from the substrate occurs, and thus there is a problem in that a yield ratio of the metal filter decreases. In addition, similarly, trapping of the CTC by using a metal filter manufactured by the electro-casting is examined (for example, refer to Patent Literature 3).